1. Field of the Invention
This invention relates generally to pavement markers, and is particularly concerned with pavement markers of the type that utilize retro-directive reflecting elements, such as cube corner reflecting elements, or other reflecting material for reflecting light from vehicles traveling over the roadway on which the pavement marker is secured. However, the invention also has use in pavement markers that are non-reflective in the sense that such markers are used only as daytime markers.
2. Description of the Prior Art
It has become common practice to delineate traffic lanes and the edges of roadways by pavement markers having retro-directive reflector elements or other relfecting material for reflecting the lights from vehicles traveling over the roadways at night. Such pavement markers are superior to painted strips on the roadway since, under poor weather conditions, painted strips on the roadway are not visible.
Generally, the reflective pavement markers are interspersed among non-reflecting pavement markers, or "daytime" markers which may be painted white, yellow or other desired colors to, for example, delineate the center line of a roadway or the dividing line between adjacent trafic lanes. As an example, every fifth pavement marker may be a "nigh-time" marker, i.e. a marker operable to reflect light rays from vehicles traveling at night, the other pavement markers serving solely as daytime markers. Typically the pavement markers are secured to the surface of the roadway by an adhesive, such as an epoxy resin. An area approximately four inches square is cleaned, as by sand blasting, and is then covered with a layer of epoxy resin. The pavement marker, either of the daytime type or night-time type, is then placed on the resin and is secured in position when the adhesive sets.
Typical examples of night-time pavement markers are disclosed in U.S. Pat. Nos. 3,332,327 and 3,409,344. The latter patents disclose pavement markers having retro-directive reflector elements of the cube corner type formed thereon. The cube corner reflector elements are formed on an outer wall of the pavement marker, which outer wall is frequently engaged by the wheels of vehicles traveling over the roadway. In order to provide adequate strength to withstand the forces imposed by the vehicle wheels, the pavement marker bodies are filled with epoxy resin or the like. In order to protect the cube corner reflector elements from moisture and chemical attack, the surface of the reflector elements are metallized. While the metallized layer performs the function of protecting the reflector elements, it also causes a loss of optical efficiency. Optical efficiency is further reduced due to the requirement that the synthetic resin wall on which the reflector elements are formed must be of great enough thickness to withstand the shock loads imposed by vehicle wheels. As the thickness of the material increases, there is greater absorption of light in the material to reduce the reflective power.